Li Wang wrote: > 2009/4/29 Tim Chase <python.l...@tim.thechases.com>: >> Li Wang wrote: >>> Hi: >>> >>> If I use an integer to represent bits: >>> e.g. 99 represents '1100011' >>> >>> How can I locate, say the second bit of 99(i.e. '1')? >>> >>> Although bin(99)[4] could be used to locate it, this transform cost >>> too much memory (99 only needs 2Bytes, while string '1100011' needs >>> 7Bytes). >>> >>> Anyone knows how to locate the second bit without using bin() function? >> You mean >> >> def get_bit(number, bit): >> return (number >> bit) & 1 >> >> ? >> > Hummm, I have tried this method too, the problem is its time > complexity. If the length of my bits is n, then the time complexity is > O(n). When I tried to implement this in practice, it did consume a lot > of time. > > So do you know how could I locate the bit in O(1) time? Transform it > into a string is a method, but takes too much space (when I try to > process a 2M file, it used more than 100M memory.....). > > Thank you very much. > >> -tkc >> >>
So... I can only conclude you are looking for bit x in the entirety of a file. First you'll have to figure out what byte to look at w/ a little integer division, then read to that point and test for the specific bit -- I'm thinking a bitwise and operation with a bit mask. Should be really fast. --David -- http://mail.python.org/mailman/listinfo/python-list
